1. Technical Field
Embodiments of the present invention relate to a unit circuit that includes an electro-optical element, such as an organic light emitting diode (hereinafter referred to sometimes as OLED), an electro-optical device, and an electronic apparatus.
2. Related Art
Display devices that use an organic light emitting diode are becoming popular. One such display device includes a plurality of pixels. Each of the pixels has an organic light emitting diode and a transistor that drives the OLED. To obtain a stable uniform display state in a plane, it is necessary to cause the organic light emitting diodes in the pixels to emit the same amount of light. However, characteristics vary among transistors, and this results in a non-uniform display state for each pixel. With the aim of solving such a problem, JP-A-2004-133240 discloses a structure that reduces an error of a threshold voltage in a drive transistor.
FIG. 14 is a circuit diagram illustrating the structure disclosed in this patent document. In the structure, first, a drive transistor Tdr is diode-connected via a transistor TrA, thereby enabling the potential of a gate (node Z2) of the drive transistor Tdr to be set at a potential (Ve1−Vth) corresponding to a threshold voltage Vth therein. This potential is held by a capacitive element Cx. Second, a data line L is electrically connected to a node Z1 of a capacitive element Cy via a transistor TrB, thereby enabling a potential of the node Z1 (gate potential of the drive transistor Tdr) to be changed with a potential Vdata of the data line L. Due to the above-described operation, the gate potential of the drive transistor Tdr varies by a level corresponding to the amount of change in the potential of the node Z1, and a supply of a current Ie1 (current that does not depend on the threshold voltage Vth) corresponding to the varied potential drives an OLED element E.
In known structures, a capacitance between a drain and a source in the transistor TrB produces capacitive coupling between the data line 1, and the node Z1, and the arrangement of elements produces capacitive coupling between the data line L and the node Z2. Therefore, if the potential of the data line L is changed by parasitic capacitors C4 and C5, the gate potential of the drive transistor Tdr undesirably varies. Crosstalk produced by such capacitive coupling is a problem for not only a single unit circuit but also between that circuit and a data line for an adjacent unit circuit.
Additionally, for known structures, since both compensation for variations in a threshold voltage and data writing are performed within a single horizontal scan period, it is difficult to obtain a sufficient period of time required for the compensation for variations in the threshold voltage. If sufficient time is spent in compensating variations in the threshold voltage, it will be difficult to accurately write data.